Wash all these ingredients in water, and then soak in water for at least six hours. Grind them fine with as much water as required, and pour the batter in to a sufficiently large vessel. Leave the batter overnight, with a pinch of soda added to the batter or a slice of bread placed on top of the batter. In the morning, the batter would have risen; remove the bread slice, and then add salt (as per taste) and mix the batter well. If batter too thick, add sufficient water. Heat a non-stick pan (or any other dosa-making pan), and then pour 1-2 spoonful of batter on to the hot pan, and make dosas. When you reverse the dosa, spread chutney and place potato palya, and then fold the dosa. You can add butter or ghee on top of the dosa.